As environmental protection laws and regulations become stringent increasingly, the demand for clean light fuels is more and more. Hydrogenation technology is an effective means for production of clean products; therefore, hydrogenation units have become standard equipment in oil refineries, and more and more hydrogenation units are used in oil refining enterprises.
The technical core of hydrogenation units lies in the application of hydrogenation catalysts. The hydrogenation function of hydrogenation catalysts comes from active metals, which are usually classified into noble metals and non-noble metals. Non-noble metals are usually used, mainly including VIB and VIII groups of metal elements (e.g., Mo, W, Ni, and Co, etc.). These metals usually exist in oxidation state in commercial hydrogenation catalysts. Metals and metal atoms in oxidation state have low hydrogenation performance, and they will exhibit high hydrogenation performance only after they are converted into sulfurized state. Therefore, to attain best hydrogenation performance of a hydrogenation catalyst, the catalyst must be sulfurized before used. Hydrogenation catalysts can be classified into sulfurized type catalysts (a sulfurizing agent is introduced into the catalyst, but the active metals are not converted into sulfurized state completely) and sulfurized-state catalysts (the active metals are converted into sulfurized state completely).
The hydrogenation process usually has to be carried out at a high temperature. During start-up process of a hydrogenation unit, the unit must be heated up from normal temperature to a higher temperature (usually ≧300° C.). Hydrogenation units are usually equipped with a heating furnace to provide heat during the start-up process and normal production process of the units. Hydrogenation reactions are usually strong exothermic reactions. In the normal production process of a hydrogenation unit, the outlet temperature of the reactor is much higher than the inlet temperature of the reactor. Thus, the materials can be heated by heat exchange without any heating furnace. However, during start-up process, since the normal hydrogenation reaction hasn't started yet, there is no heat source for heating up the unit; moreover, a heating furnace is required during start-up process since the required temperature can't be reached if any device other than a heating furnace is used. The heating furnace is a high temperature and high pressure device in the hydrogenation unit and it accounts for a large part of the equipment investment. Moreover, the heating furnace is only used during start-up process, and has a very low utilization ratio.
Patent document CN200910188142.4 discloses a sulfurizing agent supply method for wet sulfurization process of catalyst, which is mainly used for start-up process of liquid circulating hydrogenation units. With that method, a heating furnace is required. Patent document CN 200510047487.X discloses a start-up method for FCC gasoline hydro-desulfurization and olefin reduction. That method mainly utilizes reformate as sulfurized oil and can avoid the temperature rise in the sulfurization process, it is only applicable to gasoline hydrogenation units that contain zeolite catalysts.
Patent document U.S. Pat. No. 5,688,736 discloses a catalyst sulfurization method, but that method strictly forbids the use of olefin-containing start-up oil during start-up process. Patent documents CN200910188114.2, CN200910204266.7, CN200810010242.3, CN200810010245.7, CN200910204248.9, and CN200910204249.3 disclose start-up methods for hydrogenation units that utilize a sulfurized type catalyst, but those methods require an activating oil with low olefin content during start-up process, and the heat required for heating up the reaction system in the catalyst activation process has to be provided by a heating furnace. Patent document CN200910204283.0 “Start-up Method for Residual Oil Hydrotreating Process” discloses a start-up method for hydrogenation units that contain a partially sulfurized type hydrogenation guard catalyst, but the heat has to be provided by a heating furnace during start-up process.
For start-up process of hydrogenation unit that utilize a sulfurized type hydrogenation catalyst, the method that is used mostly is to introduce a start-up activating oil at low temperature and heat up the unit at a specific heating rate, till the temperature is close to the reaction starting temperature of the feedstock; then, the activating oil can be replaced by the feedstock by steps. However, a heating furnace is required during start-up process to provide the heat required for heating up the reaction system, and the energy consumption during start-up process is heavy. For units that are not equipped with a heating furnace, the start-up process can not be accomplished with that method. In addition, the system pressure drop will be increased severely and the energy consumption will be increased severely if a heating furnace is used, owing to the complex internal structure of the heating furnace.